Optimization design of passive filter's phase-frequency characteristic

In order to solve contradiction between the filter amplitude-frequency and the phase-frequency straightness, this paper proposes a filter's optimal design method. Based on the circuit designed by network synthesis method, the phase-frequency approach to a straight line using a least square method. Then optimize the circuit again by unconstrained optimization method. The simulation result indicates that this method can not only increase the filter the attenuation in stopband, but also the group delay is 12% of the total before optimized in passband, and the optimal design method is superior to the network synthesis method.